[MCParser] Add warning for zero-size .fill

[jacobly]

Summary

Adding an early return for a 0 size avoids this assertion:

llvm-mc: llvm/lib/MC/MCStreamer.cpp:135: virtual void llvm::MCStreamer::emitIntValue(uint64_t, unsigned int): Assertion `1 <= Size && Size <= 8 && "Invalid size"' failed.

[jdoerfert]

test case missing.

[arsenm]

llvm/lib/MC/MCParser/AsmParser.cpp

3357–3364

Could you just have one message with the value instead

[jacobly]

Improve warning messages.

[jacobly]

llvm/lib/MC/MCParser/AsmParser.cpp

3357–3364

Good idea.

[jacobly]

Fix typo.

[jacobly]

ping

llvm/lib/MC/MCParser/AsmParser.cpp

if (parseOptionalToken(AsmToken::Comma)) {
       ExprLoc = getTok().getLoc();
       if (parseAbsoluteExpression(FillExpr))
         return true;
     }
   }
   if (parseEOL())
     return true;
 
+  if (FillSize == 0) {
+    Warning(SizeLoc, "'.fill' directive with 0 size has no effect");
+    return false;
+  }
   if (FillSize < 0) {
     Warning(SizeLoc, "'.fill' directive with negative size has no effect");
     return false;
   }
   if (FillSize > 8) {
     Warning(SizeLoc, "'.fill' directive with size greater than 8 has been truncated to 8");
     FillSize = 8;
   }
 
   if (!isUInt<32>(FillExpr) && FillSize > 4)
     Warning(ExprLoc, "'.fill' directive pattern has been truncated to 32-bits");